As promised, collation of the list of books mentioned above, plus those that I've dug out of my attic.
Vietnam & helicopter related - factual
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Chickenhawk, Robert Mason, Corgi, 0-552-12419-2
Chickenhawk - Back to the World - Life after Vietnam, Robert Mason, pub and ISBN unknown
Wings of the Eagle, WT Grant, Ivy Books, 0-8041-1062-X
Hunter-Killer Squadron, Matthew Brennan, Pocket Books, 0-671-74453-4
Maverick, Marvicsin & Greenfield, Jove, 0-515-10662-3
Low-Level Hell, Hugh Mills, Jr., Dell, 0-440-21549-8
Centaur Flights, Richard Spalding, Ivy Books, 0-8041-1560-5
Get the bloody Job Done, Steve Eather, Allen & Unwin, 1-86448-802-6
Vietnam & Helicopter related - fictional
Let a Soldier Die, William Holland, Corgi, 0-552-12659-4
Other helicopter related
Chinook, David McMullon, Simon & Schuster, 0-684-84017-0
Weapons Free, Richard Boswell, Crecy, 0-947554-67-X
Black Hawk Down, Mark Bowden, Bantam Press, 0-593-04538-6
Others mentioned
BrandyWine's War, Vaughan and Monroe, Bartholomew House
CW2, Layne Heath, William Morrow, 0-688-05265-7
Fate is the Hunter, E.K Gann
Song of the Sky, Guy Murchie, Houghton Mifflin
Wind, Sand and Stars, Saint-Exupery
Southern Mail/Night Flight, Saint-Exupery
Sagittarius Rising, Cecil Lewis
Serenade to the Big Bird, Bert Stiles
West with the Night, Beryl Markham